Can I Use Powdered Sugar Instead Of Caster Sugar

Last Tuesday, I stood over a mixing bowl, sweating like a cartoon character who’d just seen a ghost. The recipe called for caster sugar, but my pantry was a barren wasteland of half-eaten granola bars and a bag of powdered sugar that looked as lost as I felt. I stared at the bag, then at the clock, and thought: “How different can two white powders really be?”

Spoiler alert: very different. But that’s the kind of kitchen gamble we all take at 9 PM on a Tuesday, right? So let’s break down what happens when you swap powdered sugar for caster sugar—before you end up with a crumbly disaster or a surprisingly genius hack.

The Great Sugar Identity Crisis

First, let’s get the science-y bit out of the way—I promise it’s quick. Caster sugar (also called superfine sugar) is just regular granulated sugar ground into smaller crystals. It dissolves fast, which is why it’s the king of meringues and light cakes.

Powdered sugar, on the other hand, is granulated sugar pulverized into a fine dust, mixed with a little cornstarch to keep it from clumping. That cornstarch is the sneaky troublemaker here—it changes everything.

So, can you use powdered sugar instead of caster? Technically, yes—but only if you’re ready to play Recipe Roulette. And let me tell you, the house always wins unless you know the rules.

When It Works (And When It’s a Hot Mess)

If you’re making icing, frosting, or a simple glaze, go ahead—swap away. Powdered sugar is basically built for those jobs, and the cornstarch helps thicken things nicely. Your buttercream will thank you.

Raspberry Coconut Sponge Squares - air fryer or oven

But for baking a sponge cake, meringue, or any recipe that needs structure and lift? Stop right there. The cornstarch in powdered sugar can make your cake denser than a brick, and meringues might collapse into sad, sticky puddles. I learned this the hard way, and my kitchen still hasn’t forgiven me.

Here’s a quick rule of thumb: if the recipe relies on air being beaten into the sugar (like for cookies or pavlova), stick with caster. Powdered sugar’s fine particles don’t trap air the same way—it’s like trying to fluff a pillow with sand.

The Texture Trap (You Will Notice It)

Ever bitten into a cookie that felt gritty but also somehow gummy? That’s what happens when you use powdered sugar in a standard cookie recipe. The cornstarch adds a weird, chalky layer, while the sugar’s fine dust melts too fast, leaving you with a flat, sad disc.

Castor Sugar vs. Powdered Sugar: Which One Should You Use in Baking?

On the flip side, shortbread cookies actually love powdered sugar. The cornstarch gives them that melt-in-your-mouth texture that makes them legendary. So yes, context is everything—you’re not a bad cook, you just need the right tool for the job.

If you’re staring at a recipe for whipped cream or ganache, powdered sugar can work in a pinch, but it’ll make the cream slightly heavier. Your tastebuds won’t scream, but your texture game will be off by a whisper.

The Emergency Conversion (Because I Know You’re Desperate)

Okay, fine—you’re already elbow-deep in flour and you refuse to run to the store. I respect that. Here’s the hack: you can make caster sugar from granulated sugar by blitzing it in a food processor for 10-15 seconds. Boom—done. No cornstarch, no tears.

Granulated Sugar Vs Caster Sugar What Is Caster Sugar And How To Make

But if you only have powdered sugar and must use it for a cake? Use 1 cup powdered sugar for every 1 cup caster sugar, but reduce the liquid in the recipe by a tablespoon or two to compensate for the cornstarch. Your cake might still be a bit denser, but it’ll be edible—and that’s a win.

Oh, and never try to use powdered sugar in a recipe that calls for creaming butter and sugar. The fine particles won’t create that fluffy, airy paste you need. Your mixer will whine, and you’ll be left with a sad, greasy blob.

The Bottom Line (No Sugarcoating)

So can you use powdered sugar instead of caster sugar? Sure—if you’re okay with a slightly different texture, a denser bake, and a tiny bit of cornstarch flavor. In dark chocolate recipes or heavy batters, you might not even notice. But in light, delicate bakes? You’ll hear your grandmother’s ghost tut from the afterlife.

My advice? Keep both in your pantry, but when in doubt, take the extra two minutes to grind your own sugar. Your future self—and your cake—will send you a thank-you note. Or, you know, just eat the powdered sugar straight from the bag like I did. No judgment here.